Inter-network magnetic fields observed with sub-arcsec resolution

Abstract

We analyze a time sequence of Inter-Network (IN) magnetograms observed at the solar disk center. Speckle reconstruction techniques provide a good spatial resolution (0.″5 cutoff frequency) yet maintaining a fair sensitivity (some 20 G). Patches with signal above noise cover 60% of the observed area, most of which corresponds to intergranular lanes. The large surface covered by signal renders a mean unsigned magnetic flux density between 17 G and 21 G (1 G ≡ 1 Mx cm-2). The difference depends on the spectral line used to generate the magnetograms (FeIλ6302.5 Å or FeIλ6301.5 Å). Such systematic difference can be understood if the magnetic structures producing the polarization have intrinsic field strengths exceeding 1 kG, and consequently, occupying only a very small fraction of the surface (some 2%). We observe both, magnetic signals changing in time scales smaller than 1 min, and a persistent pattern lasting longer than the duration of the sequence (17 min). The pattern resembles a network with a spatial scale between 5 and 10 arcsec, which we identify as the mesogranulation. The strong dependence of the polarization signals on spatial resolution and sensitivity suggests that much quiet Sun magnetic flux still remains undetected.